Impact of Attenuation Coefficient on Urban Storm Sewer System Desining

Abstract:

Based on the Code for Design of Outdoor Wastewater Engineering,calculating storm sewer design flow (Q) with an attenuation coefficient (m) leads to a lower design flow than that of projects abroad,and reduces the capacity for disaster resistance of urban storm sewer system for the same design standard.This manuscript focuses on discussing the impacts of flow attenuation coefficient (m) on storm sewer system design.Based on appropriate assumptions,the mathematical expressions of the relationship between return periods with m=1 and m=2 were deduced,which lays the theoretical foundation for the analysis of the relationship among return periods.According to several examples,it is confirmed that the design flow rates defined by m=1,design return period at one year (P=1) and with same time intervals,could reach the same level as in the case with P=1.531 ～4.028 years when m=2 is taken.Reversely,when m=2 and P=1 year,the design flows are approximately equivalent to the values in situations with m=1 and P=0.69 ～0.393 years.In conclusion,the research suggests that the use of an attenuation coefficient would result in substantial reduction in storm sewer system design criteria and consequently increase the risk of waterlogging in urban regions in China.